1. Field of the Invention
This invention relates to an engine-starting discrimination system for a hybrid vehicle, more particularly to a system for discriminating whether the engine has definitely been started by a generator-motor mounted on a hybrid vehicle.
2. Description of the Related Art
Hybrid vehicles that combine a generator-motor and an internal combustion engine are of two general types: series hybrid vehicles whose wheels are driven solely by an electric motor (generator-motor) and parallel hybrid vehicles whose wheels are driven by either or both an electric motor (generator-motor) and an internal combustion engine. In this kind of vehicle, no matter whether the vehicle is a series hybrid one or a parallel hybrid one, the generator-motor is used as a starter motor to start the internal combustion engine.
In the hybrid vehicle, the engine is started automatically during vehicle running, in other words, engine starting is conducted without the vehicle operator's participation. Moreover, the generator-motor in the hybrid vehicle cranks the engine at a speed relatively higher than an ordinary starter motor and thus, the generator-motor can assist torque to start the engine at a speed close to the engine idling speed. For these reasons, it has been difficult in the hybrid vehicle to discriminate whether the engine is definitely started.
Japanese Laid-Open Patent Application No. Hei 8(1996)-261,118 teaches starting the engine by increasing the torque command value supplied to the generator-motor gradually and then decreasing the torque command value to zero so as to cancel the torque assist. The engine speed is detected and if the engine speed does not drop under this no-torque-assist situation, it is discriminated that the engine is definitely started.
Japanese Laid-Open Patent Application No. Hei 9(1997)-117,012 discloses supplying current to the generator-motor to rotate the engine to start and similarly discontinuing the torque assist when the engine speed has reached an engine idling speed or thereabout. Then the engine speed is detected after a predetermined time has elapse and if the detected engine speed is at or above a reference speed, it is discriminated that the engine is definitely started.
Since, however, the prior art system disclosed in Japanese Laid-Open Patent Application No. Hei 8(1996)-261,118, determines whether the engine is definitely started based on the engine speed after the torque assistance has been discontinued, it can not discriminate accurately whether the engine revolution is due to the successful starting or due to the inertial force created by the previous torque assistance. Thus, the prior art system can not discriminates the engine starting with high accuracy. Moreover, the prior art system is disadvantageous in fuel consumption, since it involves unnecessary cranking.
These problems will also be applied to the other prior art described in Japanese Laid-Open Patent Application No. Hei 9(1997)-117,012, since it discriminates the engine starting based on the engine speed after a predetermined time from the discontinuation of torque assistance. Moreover, since this prior art needs more time to wait the engine speed detection, the discrimination is disadvantageously delayed by the waiting time.